#!/usr/bin/node

const log=console.log,
      arg=process.argv[2];

if(typeof(arg) === 'undefined' ||
    arg === '--help' || 
    arg === '-h') {
  help();
} else {
  cale();
}

function help(){
  const msg = ''
    + 'usage: cmd-name [OPTION] [expression]\n'
    + 'evaluate the expression.\n'
    + '\n'
    +'Mandatory arguments to long options are mandatory for short options too.\n'
    +' -h, --help output help information and exit\n';

  log(msg);
}

function cale(){
  try{
    log(`${arg}=${eval(arg)}`);
  }catch(e){
    console.error(`${arg} 不是合法的数学表达式！`);
  }
}
